661165 has 4 divisors (see below), whose sum is σ = 793404. Its totient is φ = 528928.

The previous prime is 661139. The next prime is 661183. The reversal of 661165 is 561166.

661165 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 561166 = 2 ⋅280583.

It can be written as a sum of positive squares in 2 ways, for example, as 249001 + 412164 = 499^2 + 642^2 .

It is a cyclic number.

It is not a de Polignac number, because 661165 - 2¹⁷ = 530093 is a prime.

It is a super-3 number, since 3×661165³ = 867063332660001375, which contains 333 as substring.

It is an Ulam number.

It is a Duffinian number.

661165 is a lucky number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 66112 + ... + 66121.

It is an arithmetic number, because the mean of its divisors is an integer number (198351).

2⁶⁶¹¹⁶⁵ is an apocalyptic number.

It is an amenable number.

661165 is a deficient number, since it is larger than the sum of its proper divisors (132239).

661165 is a wasteful number, since it uses less digits than its factorization.

661165 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 132238.

The product of its digits is 1080, while the sum is 25.

The square root of 661165 is about 813.1205322706. The cubic root of 661165 is about 87.1170749543.

Subtracting from 661165 its reverse (561166), we obtain a palindrome (99999).

The spelling of 661165 in words is "six hundred sixty-one thousand, one hundred sixty-five".